The invention relates to a method and apparatus useful in the assay of DNA or RNA and is particularly concerned with multiwell filtration devices capable of performing a plurality of assays simultaneously.
Test plates for in vitro analysis which contain a multiplicity of individual wells or reaction chambers are commonly known laboratory tools. Such devices have been employed for a broad variety of purposes and assays as are exemplified by U.S. Pat. Nos. 3,649,464; 4,304,865; 4,276,048; 4,154,795; and Re 30,562. Microporous membrane filters and filtration devices containing such microporous membranes have become especially useful with many of the recently developed cell and tissue culture techniques and assays - particularly those in the fields of virology and immunology.
Multi-well filtration plates have been used to conduct multiple assays simultaneously some of which last several hours before filtration is actually performed. With such filtration plates, especially those containing microporous membranes, there is a well recognized and recurrent problem in that fluids in the wells tend to pass through the membrane by gravity flow thereby causing a loss of contents from within the reaction well before the desired stage in the experimental design. Membranes at the bottom of wells in other devices lose liquid by gravity flow and also by lateral migration to adjacent wells thereby causing cross-contamination. Prevention of fluid loss through the membrane in this manner is vitally important when the assay utilizes very small sample volumes as reactants, since such test samples often are less than 100 microliters in volume. The pendant drop that invariably forms on the underside of the microporous membrane due to such capillary action and gravity flow is typically about 50 microliters in volume and it is apparent that a fluid loss of such proportions must drastically affect the assay.
Presently, there are available hybridization techniques for detecting single strand DNA or RNA molecules including single strand viral DNA or RNA molecules. Generally hybridization involves the steps of binding single strand DNA or RNA molecules to a substrate such as nitrocellulose and thereafter mixing the bound DNA or RNA with a liquid containing labeled complementary single strand DNA or RNA molecules. The degree of binding of the complementary single strand DNA molecules is measured by measuring the amount of marker on the substrate. By operating in this manner, it is possible to assay for either the single strand DNA or RNA bound to the substrate or the DNA or RNA in the liquid. Such a technique is described, for example, in U.S. Pat. No. 4,302,204. Prior to the present invention, there has been no efficient and reliable method to assay for the presence of virus in the blood. This is primarily due to interference of the hybridization reaction by a variety of blood serum proteins.
Accordingly, it would be desirable to provide an efficient and reliable method to assay for virus, particularly for virus in blood.